Andre, I don't think my comment is that far-fetched. He is a top-quality defender and the facts back my statement. Aside from my objective reference from "whoscored.com", which is a very credible stats resource, how does this read?
Maicon:
UEFA Europa League: 2010–11
Portuguese League: 2010–11, 2011–12, 2012–13
Portuguese Cup: 2009–10, 2010–11
Portuguese Supercup: 2009, 2010, 2011, 2012, 2013
UEFA Super Cup: Runner-up 2011
Portuguese League Cup: Runner-up 2009–10, 2012–13
And he's only 25. He was a starter every year except last, when he was out for most of the year with a major injury. Do those seem like a mediocre 25 year old's accomplishments? As for Garay and Mangala, those guys are top quality, no question. But, you are not using context as part of your argument.
Mangala was highly sought because he managed to break into the French national team and because he is a very physical player. Garay for his part, broke into the Argentine national team starting lineup. Think that's not a big deal? What did we all think of Rojo before this summer? Mediocre, right? Now he's a Man U player valued at $20 million.
Also, and perhaps MOST important, Mangala and Garay have the same management team. Would you like to know who else is a client of this team? Ok:
Ronaldo, James, Falcao, Di Maria, Diego Costa, Pepe, Nani, Ricardo Carvalho, and Deco, to name but a few. Maicon's management? They also handle Fernando, Rafa Silva and a few bartenders. So, is this any coincidence? One team has ALL the highest transfer valued players of the last 5 years. The other has some good players.
Also, Garay, despite your "props" went for a measley $6 million. So, there's that. Which doesn't exactly boost your argument. What's my point? There are more factors that decide how much a player is sought after or valued, other than just how good they are.
Maicon is excellent, and has been for a long time. I will be sad on the day Porto sell him, but I will take solace in the fact that if they sell him for $6,000,000.01, he will have been sold for more money than Garay, and therefore (by your own flawless logic), a better player than him.